Evaluation Of Rice Genotypes And Changes Defence Responses

Rice (Oryza sativa L.) is a principal source of staple food for most of the world populations particularly in Asia. Several plant nematodes are reported to cause yield loss in rice crop among them rice root knot nematode, Meloidogyne graminicola is one of the main constraint to alleviate the yield of rice. After entering of nematode into the host switch on basal and constitutive defence related responses mediated by several pathways such as salicylic acid, jasmonic acid, ethylene, etc. In the present study, selected 36 rice genotypes were screened against M. graminicola under in vitro conditions to evaluate resistance.

It was found that Phule Radha, EK70 and Khalibagh were highly resistant where producing least number of galls. Halvi Sal 17 was most susceptible genotype and used as control check. The multiplication value of M. graminicola in Phule Radha, EK70 and Khalibagh were very less as comparison to in Halvi Sal 17. Upon screening of selected resistant/susceptible genotypes under greenhouse conditions (soil), Phule Radha was found to be highly resistant and Halvi Sal 17 most susceptible genotype. Investigation of plant defence responsive genes involved in various pathways was done in resistant and susceptible genotypes. Based on our experiment, it is divulged that upon invasion of M. graminicola, expression of MAPK20, ICS1, NPR1, PAD4, AOS2, JAMYB, and ACO7 involved in distinct pathways activated in resistant genotype while downregulation of those genes observed in susceptible genotype. All over it shows that Phule Radha is highly resistant to nematode, in addition to that this genotype reported to moderately resistant to blast and bacterial leaf blight. This genotype could be a superior option for gene pyramiding to develop genotype with multiple resistant genes.

Introduction

Rice is one of the important cereals with respect to production as well as major human food crop, majority of the world population depend on rice every day and gathered more attention in the field of nematology to studying various interactions (physiological and molecular) between rice and plant parasitic nematodes (PPNs). Plant nematodes are causing 173 $US billion losses annually to the world agriculture. In rice, the economic loss caused estimated about 20% due to PPNs. Rice plants attacked by several plant nematodes among them few are caused substantial loss to this crop. The rice root knot nematode (RRKN), Meloidogyne graminicola widely present in rice field and contemplate a major constraint and causing considerable yield loss in rice growing area of Southeast Asia and other rice growing countries. Yield loss caused by M. graminicola in rice crop has been reported about 16-32%. Upon hatching from the eggs, infective juveniles of sedentary nematodes attracted towards the host root. Generally juveniles of root knot nematodes penetrate at meristematic zone of the root surface and proceed intercellularly within the root system. Some cells of the vascular tissue infected by root knot nematode are transformed to nematode feeding site generally known as “giant cells”. The giant cells comprises of dense cytoplasm with substantial number organelles, multiple nuclei, central vacuole, thickened cell wall with feeding tubes. The cells which are adjacent to the giant cells developed through hyperplasia and hypertrophied form a knot like structure on the root surface of the host plant. Host plant generally exposed to biotic as well as abiotic stress among them biotic stress obtained from insect, nematodes, fungi, bacteria, and viruses. Degree of pathogenesis can be modulated by the interaction between pathogen and their host plant.

Resistant plants has a potential to confront the pathogens and established defence mechanisms against them. Pathogen and host plant intercommunicate with each other which explained by ‘zigzag’ model where plants having ability to rectify pathogen-associated molecular pattern (PAMPs) acquire from pathogen exploiting pattern recognition receptors (PRRs) begin to pattern-triggered immunity (PTI). Upon entry of PPNs into the host plant activates the constitutive and basal defence responses in host which is regulated by expression of different defence signalling pathways, consist of plant hormones (salicylic acid, SA; ethylene, ET; jasmonic acid, JA), pathogenesis-related (PR) proteins, and different plant transcription factors; and end result of this signalling responses regulate the susceptibility/resistance of plants to PPNs. SA signalling most essential in R-gene encoded defence response against sedentary endoparasitic nematodes. In Arabidopsis lox4 mutant, susceptibility of root knot nematodes occurring upon induction of JA biosynthesis genes which shows the association between JA accumulation and susceptibility of root knot nematodes. Therefore JA biosynthesis genes playing a key role in plant susceptibility to nematode. ET biosynthesis and its signalling play an important role in susceptibility as well as resistance against sedentary nematodes which differ according to the particular nematode infected.

Kumari et al. (2016) distinguished susceptible and resistant cultivars of rice in PF-127 medium upon inoculation of M. graminicola and comparable articulation of various defence related genes were examined in local as well as in systemic plant tissues. Information associated with the function of plant hormones which require for induction of systemic and local defence in monocotyledon plant upon invasion of PPNs is very narrow. In order to reduce the yield loss caused by M. graminicola in rice, it is necessary to seeking new resistance sources to manage this nematode effectively. Therefore study was managed with an objective of evaluation of rice genotypes and changes in stress related defence responses to combat RRKN.